Heatable windshield

BACKGROUND OF THE INVENTION

00011. Field of the Invention

0002This invention relates generally to vehicle transparencies, such as vehicle windshields, and, in one particular embodiment, to a heatable vehicle windshield.

00032. Technical Considerations

0004It has been known to pass electric current through a conductor (e.g., a wire or an electrically conductive coating) on a laminated vehicle windshield in order to raise the temperature of the windshield. This is particularly useful in colder climates for defogging and to melt ice and snow on the windshield.

0005In wire-heated windshields, fine electrically-conductive wires are placed between the windshield plies. The wires are connected to a power source, such as a conventional 14 volt (v) vehicle alternator. The wires have sufficiently low resistance to provide the windshield with a power density of 5 to 7 watts per decimeter squared (W/dm²).

0006However, a problem with wire-heated windshields is that the wires can be seen by the vehicle occupants. The presence of these wires can be aesthetically undesirable and can interfere with visibility through the windshield. If the diameter of the wires is decreased to try to reduce the visibility of the wires, the number of wires must be increased to maintain the desired power density. The increased number of wires adversely decreases the total solar energy transmitted (TSET) of the windshield. If the height of the windshield increases, the wires must be longer to maintain the desired power density. These longer wires are also undesirable with respect to windshield aesthetics and/or transmittance.

0007In an effort to address this problem, some heated windshields utilize transparent, conductive coatings rather than wires to heat the windshield. While these known transparent coatings overcome the aesthetic and visibility problems associated with the use of wires, conventional heated windshield coatings also have some drawbacks. For example, conventional heated windshield coatings typically have a sheet resistance of 2 ohms per square (Ω/□) or greater. A conventional 14v (80 ampere; 1,120 watts) alternator does not provide sufficient voltage to power a conventional heated windshield coating to a temperature sufficient for de-icing. Therefore, for vehicles with these conventional coatings, the vehicles must be altered to increase the available voltage. One way to do this is to replace the conventional 14v (1,120 W) alternator with a 42v (2,500 W to 5,000 W) alternator. Another way to address this problem is to maintain the conventional 14v alternator but add a DC to DC converter to step up the voltage to a sufficient level, e.g., 42v, to heat the windshield to a commercially acceptable level.

0008However, replacing the conventional 14v alternator or adding a DC to DC converter increases the cost and complexity of the vehicle electrical system. Also, as one skilled in the art will appreciate, all things being equal, a system that functions on 14 volts is typically safer to operate than one that operates on 42 volts.

0009Therefore, it would be desirable to provide a transparency, such as a laminated vehicle transparency, that reduces or eliminates at least some of the problems associated with conventional heatable transparencies.

SUMMARY OF THE INVENTION

0010A heatable transparency of the invention comprises a first ply having a No. <b>1</b> surface and a No. <b>2</b> surface and a second ply having a No. <b>3</b> surface and a No. <b>4</b> surface. The No. <b>2</b> surface faces the No. <b>3</b> surface. A conductive coating is formed on the No. <b>2</b> or No. <b>3</b> surface. A power supply is in contact with the conductive coating. The system is configured such that the power supply provides less than 42 volts to the conductive coating. In one non-limiting embodiment, the system is configured such that the power supply provides less than 24 volts, such as in the range of 13 volts to 15 volts to the conductive coating. In one non-limiting embodiment, the coating provides a power density in the range of 4 W/dm²to 8 W/dm², e.g., 5 W/dm²to 7 W/dm².

0011A further heatable transparency comprises a first ply having a No.<b>1</b> surface and a No. <b>2</b> surface and a second ply having a No. <b>3</b> surface and a No. <b>4</b> surface. The No. <b>2</b> surface faces the No. <b>3</b> surface. A conductive coating is formed on the No. <b>2</b> or No. <b>3</b> surface, with the conductive coating comprising three or more metallic silver layers. An antireflective coating can be formed on the No. <b>4</b> surface.

0012A further heatable laminated transparency comprises a first ply having a No. <b>1</b> surface and a No. <b>2</b> surface and a second ply having a No. <b>3</b> surface and a No. <b>4</b> surface. The No. <b>2</b> surface faces the No. <b>3</b> surface. A conductive coating is formed on the No. <b>2</b> or No. <b>3</b> surface. The conductive coating comprises three or more metallic silver layers and the conductive coating is configured to provide a resistivity in the range of 0.6 Ω/□ to 1.70 Ω/□. An antireflective coating is formed on the No. <b>4</b> surface. In one embodiment, the antireflective coating comprises at least one zinc stannate layer and at least one zinc oxide layer. The laminated transparency can have a visible light transmittance of greater than or equal to 70% at a reference wavelength of 550 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

0013The invention will be described with reference to the following drawing figures wherein like reference numbers identify like parts throughout.

0014<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view (not to scale) of a heatable windshield incorporating features of the invention;

0015<figref idref="DRAWINGS">FIG. 2</figref> is an expanded view (not to scale) of the windshield taken along the line II-II of <figref idref="DRAWINGS">FIG. 1</figref>;

0016<figref idref="DRAWINGS">FIG. 3</figref> is a cross-sectional view (not to scale) of a non-limiting conductive coating suitable for the invention;

0017<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view (not to scale) of a non-limiting antireflective coating suitable for the invention; and

0018<figref idref="DRAWINGS">FIG. 5</figref> is a schematic view (not to scale) of another windshield incorporating features of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0019As used herein, spatial or directional terms, such as “left”, “right”, “inner”, “outer”, “above”, “below”, and the like, relate to the invention as it is shown in the drawing figures. However, it is to be understood that the invention can assume various alternative orientations and, accordingly, such terms are not to be considered as limiting. Further, as used herein, all numbers expressing dimensions, physical characteristics, processing parameters, quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical values set forth in the following specification and claims may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical value should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass the beginning and ending range-values and any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, e.g., 1 to 3.3, 4.7 to 7.5, 5.5 to 10, and the like. Further, as used herein, the terms “formed over”, “deposited over”, or “provided over” mean formed, deposited, or provided on but not necessarily in contact with the surface. For example, a coating layer “formed over” a substrate does not preclude the presence of one or more other coating layers or films of the same or different composition located between the formed coating layer and the substrate. As used herein, the terms “polymer” or “polymeric” include oligomers, homopolymers, copolymers, and terpolymers, e.g., polymers formed from two or more types of monomers or polymers. The terms “visible region” or “visible light” refer to electromagnetic radiation having a wavelength in the range of 380 nm to 800 nm. The terms “infrared region” or “infrared radiation” refer to electromagnetic radiation having a wavelength in the range of greater than 800 nm to 100,000 nm. The terms “ultraviolet region” or “ultraviolet radiation” mean electromagnetic energy having a wavelength in the range of 300 nm to less than 380 nm. Additionally, all documents, such as but not limited to issued patents and patent applications, referred to herein are to be considered to be “incorporated by reference” in their entirety. The “visible transmittance” and “dominant wavelength” values are those determined using the conventional methods. Those skilled in the art will understand that properties such as visible transmittance and dominant wavelength can be calculated at an equivalent standard thickness, e.g., 5.5 mm, even though the actual thickness of a measured glass sample is different than the standard thickness.

0020For purposes of the following discussion, the invention will be discussed with reference to use with a vehicle transparency, in particular an automotive windshield. However, it is to be understood that the invention is not limited to use with vehicle windshields but could be practiced in any desired field, such as but not limited to laminated or non-laminated residential and/or commercial windows, insulating glass units, and/or transparencies for land, air, space, above water and under water vehicles, e.g., automotive windshields, sidelights, back lights, sunroofs, and moon roofs, just to name a few. Therefore, it is to be understood that the specifically disclosed exemplary embodiments are presented simply to explain the general concepts of the invention and that the invention is not limited to these specific exemplary embodiments. Additionally, while a typical vehicle “transparency” can have sufficient visible light transmittance such that materials can be viewed through the transparency, in the practice of the invention the “transparency” need not be transparent to visible light but may be translucent or opaque (as described below). Non-limiting examples of vehicle windshields and methods of making the same are found in U.S. Pat. Nos. 4,820,902; 5,028,759; and 5,653,903.

0021A non-limiting heatable transparency <b>10</b> (e.g., automotive windshield) incorporating features of the invention is illustrated in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>. The transparency <b>10</b> can have any desired visible light, infrared radiation, or ultraviolet radiation transmission and reflection. For example, the transparency <b>10</b> can have a visible light transmission of any desired amount, e.g., greater than 0% to 100%, e.g., greater than 70%. For windshield and front sidelight areas in the United States, the visible light transmission is typically greater than or equal to 70%. For privacy areas, such as rear seat sidelights and rear windows, the visible light transmission can be less than that for windshields, such as less than 70%.

0022As best seen in <figref idref="DRAWINGS">FIG. 2</figref>, the transparency <b>10</b> includes a first ply <b>12</b> with a first major surface facing the vehicle exterior, i.e., an outer major surface <b>14</b> (No. <b>1</b> surface) and an opposed second or inner major surface <b>16</b> (No. <b>2</b> surface). The transparency <b>10</b> also includes a second ply <b>18</b> having an outer (first) major surface <b>20</b> (No. <b>3</b> surface) and an inner (second) major surface <b>22</b> (No. <b>4</b> surface). This numbering of the ply surfaces is in keeping with conventional practice in the automotive art. The first and second plies <b>12</b>, <b>18</b> can be bonded together in any suitable manner, such as by a conventional interlayer <b>24</b>. Although not required, a conventional edge sealant can be applied to the perimeter of the laminated transparency <b>10</b> during and/or after lamination in any desired manner. A decorative band, e.g., an opaque, translucent or colored shade band <b>26</b> (shown in <figref idref="DRAWINGS">FIG. 2</figref>), such as a ceramic band, can be provided on a surface of at least one of the plies <b>12</b>, <b>18</b>, for example around the perimeter of the inner major surface <b>16</b> of the first ply <b>12</b>. An electrically conductive coating <b>30</b> is formed over at least a portion of one of the plies <b>12</b>, <b>18</b>, such as over the No. <b>2</b> surface <b>16</b> or No. <b>3</b> surface <b>20</b>. An antireflective coating <b>32</b> is formed over at least one of the surfaces, such as over the No. <b>4</b> surface <b>22</b>. A bus bar assembly <b>36</b> (<figref idref="DRAWINGS">FIG. 1</figref>) is in electrical contact with the conductive coating <b>30</b>. The bus bar assembly <b>36</b> is also connected to an electrical power source <b>38</b> (<figref idref="DRAWINGS">FIG. 1</figref>) and will be discussed in more detail below. In one non-limiting aspect of the invention, the power source <b>38</b> can be a conventional vehicle alternator, e.g., configured to supply approximately 14 volts. Thus, in the practice of one non-limiting embodiment of the invention, no DC to DC power converter is present, as is required in the known art.

0023In the broad practice of the invention, the plies <b>12</b>, <b>18</b> of the transparency <b>10</b> can be of the same or different materials. The plies <b>12</b>, <b>18</b> can include any desired material having any desired characteristics. For example, one or more of the plies <b>12</b>, <b>18</b> can be transparent or translucent to visible light. By “transparent” is meant having visible light transmittance of greater than 0% to 100%. Alternatively, one or more of the plies <b>12</b>, <b>18</b> can be translucent. By “translucent” is meant allowing electromagnetic energy (e.g., visible light) to pass through but diffusing this energy such that objects on the side opposite the viewer are not clearly visible. Examples of suitable materials include, but are not limited to, plastic substrates (such as acrylic polymers, such as polyacrylates; polyalkylmethacrylates, such as polymethylmethacrylates, polyethylmethacrylates, polypropylmethacrylates, and the like; polyurethanes; polycarbonates; polyalkylterephthalates, such as polyethyleneterephthalate (PET), polypropyleneterephthalates, polybutyleneterephthalates, and the like; polysiloxane-containing polymers; or copolymers of any monomers for preparing these, or any mixtures thereof); ceramic substrates; glass substrates; or mixtures or combinations of any of the above. For example, one or more of the plies <b>12</b>, <b>18</b> can include conventional soda-lime-silicate glass, borosilicate glass, or leaded glass. The glass can be clear glass. By “clear glass” is meant non-tinted or non-colored glass. Alternatively, the glass can be tinted or otherwise colored glass. The glass can be annealed or heat-treated glass. As used herein, the term “heat treated” means tempered or at least partially tempered. The glass can be of any type, such as conventional float glass, and can be of any composition having any optical properties, e.g., any value of visible transmission, ultraviolet transmission, infrared transmission, and/or total solar energy transmission. By “float glass” is meant glass formed by a conventional float process in which molten glass is deposited onto a molten metal bath and controllably cooled to form a float glass ribbon. The ribbon is then cut and/or shaped and/or heat treated as desired. Examples of float glass processes are disclosed in U.S. Pat. Nos. 4,466,562 and 4,671,155. The first and second plies <b>12</b>, <b>18</b> can each be, for example, clear float glass or can be tinted or colored glass or one ply <b>12</b>, <b>18</b> can be clear glass and the other ply <b>12</b>, <b>18</b> colored glass. Although not limiting to the invention, examples of glass suitable for the first ply <b>12</b> and/or second ply <b>18</b> are described in U.S. Pat. Nos. 4,746,347; 4,792,536; 5,030,593; 5,030,594; 5,240,886; 5,385,872; and 5,393,593. The first and second plies <b>12</b>, <b>18</b> can be of any desired dimensions, e.g., length, width, shape, or thickness. In one exemplary automotive transparency, the first and second plies can each be 1 mm to 10 mm thick, e.g., 1 mm to 5 mm thick, or 1.5 mm to 2.5 mm, or 1.8 mm to 2.3 mm. In one non-limiting embodiment, the first ply <b>12</b> and/or second ply <b>18</b> can have a visible light transmittance of greater than 90%, such as greater than 91%, at a reference wavelength of 550 nm. The glass composition for the first ply <b>12</b> and/or second ply <b>18</b> can have a total iron content in the range of greater than 0 wt. % to 0.2 wt. % and/or a redox ratio in the range of 0.3 to 0.6.

0024In one non-limiting embodiment, one or both of the plies <b>12</b>, <b>18</b> may have a high visible light transmittance at a reference wavelength of 550 nanometers (nm). By “high visible light transmittance” is meant visible light transmittance at 550 nm greater than or equal to 85%, such as greater than or equal to 87%, such as greater than or equal to 90%, such as greater than or equal to 91%, such as greater than or equal to 92%, at 5.5 mm equivalent thickness for glass from 2 mm to 25 mm sheet thickness. Particularly useful glass for the practice of the invention is disclosed in U.S. Pat. Nos. 5,030,593 and 5,030,594 and is commercially available from PPG Industries, Inc. under the mark Starphire®.

0025The interlayer <b>24</b> can be of any desired material and can include one or more layers or plies. The interlayer <b>24</b> can be a polymeric or plastic material, such as, for example, polyvinylbutyral, plasticized polyvinyl chloride, or multi-layered thermoplastic materials including polyethyleneterephthalate, etc. Suitable interlayer materials are disclosed, for example but not to be considered as limiting, in U.S. Pat. Nos. 4,287,107 and 3,762,988. The interlayer <b>24</b> secures the first and second plies <b>12</b>, <b>18</b> together, provides energy absorption, reduces noise, and increases the strength of the laminated structure. The interlayer <b>24</b> can also be a sound-absorbing or attenuating material as described, for example, in U.S. Pat. No. 5,796,055. The interlayer <b>24</b> can have a solar control coating provided thereon or incorporated therein or can include a colored material to reduce solar energy transmission.

0026The coating <b>30</b> is an electrically conductive coating deposited over at least a portion of a major surface of one of the glass plies <b>12</b>, <b>18</b>, such as on the inner surface <b>16</b> of the outboard glass ply <b>12</b> (<figref idref="DRAWINGS">FIG. 2</figref>) or the outer surface <b>20</b> of the inner glass ply <b>18</b>. The conductive coating <b>30</b> can include one or more metallic films positioned between pairs of dielectric layers applied sequentially over at least a portion of one of the glass plies <b>12</b>, <b>18</b>. The conductive coating <b>30</b> can be a heat and/or radiation reflecting coating and can have one or more coating layers or films of the same or different composition and/or functionality. As used herein, the term “film” refers to a coating region of a desired or selected coating composition. A “layer” can comprise one or more “films” and a “coating” or “coating stack” can comprise one or more “layers”. For example, the conductive coating <b>30</b> can be a single layer coating or a multi-layer coating and can include one or more metals, non-metals, semi-metals, semiconductors, and/or alloys, compounds, compositions, combinations, or blends thereof. For example, the conductive coating <b>30</b> can be a single layer metal oxide coating, a multiple layer metal oxide coating, a non-metal oxide coating, a metallic nitride or oxynitride coating, a non-metallic nitride or oxynitride coating, or a multiple layer coating comprising one or more of any of the above materials. In one non-limiting embodiment, the conductive coating <b>30</b> can be a doped metal oxide coating.

0027The coating <b>30</b> can be a functional coating. As used herein, the term “functional coating” refers to a coating that modifies one or more physical properties of the substrate over which it is deposited, e.g., optical, thermal, chemical or mechanical properties, and is not intended to be entirely removed from the substrate during subsequent processing. The conductive coating <b>30</b> can have one or more functional coating layers or films of the same or different composition or functionality.

0028The conductive coating <b>30</b> can be, for example, an electrically conductive coating used to make heatable windows as disclosed in U.S. Pat. Nos. 5,653,903 and 5,028,759, or a single-film or multi-film coating used as an antenna. Likewise, the conductive coating can be a conductive, solar control coating. As used herein, the term “solar control coating” refers to a coating comprised of one or more layers or films that affect the solar properties of the coated article, such as but not limited to the amount of solar radiation, for example, visible, infrared, or ultraviolet radiation, reflected from, absorbed by, or passing through the coated article, shading coefficient, emissivity, etc. The solar control coating can block, absorb or filter selected portions of the solar spectrum, such as but not limited to the IR, UV, and/or visible spectrums. Examples of solar control coatings that can be used in the practice of the invention are found, for example but not to be considered as limiting, in U.S. Pat. Nos. 4,898,789; 5,821,001; 4,716,086; 4,610,771; 4,902,580; 4,716,086; 4,806,220; 4,898,790; 4,834,857; 4,948,677; 5,059,295; and 5,028,759, and also in U.S. patent application Ser. No. 09/058,440.

0029The conductive coating <b>30</b> can also be an electroconductive low emissivity coating that allows visible wavelength energy to be transmitted through the coating but reflects longer wavelength solar infrared energy. By “low emissivity” is meant emissivity less than 0.4, such as less than 0.3, such as less than 0.2, such as less than 0.1, e.g., less than or equal to 0.05. Examples of low emissivity coatings are found, for example, in U.S. Pat. Nos. 4,952,423 and 4,504,109 and British reference GB 2,302,102.

0030Non-limiting examples of suitable conductive coatings <b>30</b> for use with the invention are commercially available from PPG Industries, Inc. of Pittsburgh, Pa. under the SUNGATE® and SOLARBAN® families of coatings. Such coatings typically include one or more antireflective coating films comprising dielectric or anti-reflective materials, such as metal oxides or oxides of metal alloys, which are transparent to visible light. The conductive coating <b>30</b> can also include one or more infrared reflective films comprising a reflective metal, e.g., a noble metal such as gold, copper or silver, or combinations or alloys thereof, and can further comprise a primer film or barrier film, such as titanium, as is known in the art, located over and/or under the metal reflective layer. The conductive coating <b>30</b> can have any desired number of infrared reflective films, such as but not limited to 1 to 5 infrared reflective films. In one non-limiting embodiment, the coating <b>30</b> can have 1 or more silver layers, e.g., 2 or more silver layers, e.g., 3 or more silver layers, such as 5 or more silver layers. A non-limiting example of a suitable coating having three silver layers is disclosed in U.S. patent application Ser. No. 10/364,089 (Publication No. 2003/0180547 A1).

0031The conductive coating <b>30</b> can be deposited by any conventional method, such as but not limited to conventional chemical vapor deposition (CVD) and/or physical vapor deposition (PVD) methods. Examples of CVD processes include spray pyrolysis. Examples of PVD processes include electron beam evaporation and vacuum sputtering (such as magnetron sputter vapor deposition (MSVD)). Other coating methods could also be used, such as but not limited to sol-gel deposition. In one non-limiting embodiment, the conductive coating <b>30</b> can be deposited by MSVD. Examples of MSVD coating devices and methods will be well understood by one of ordinary skill in the art and are described, for example, in U.S. Pat. Nos. 4,379,040; 4,861,669; 4,898,789; 4,898,790; 4,900,633; 4,920,006; 4,938,857; 5,328,768; and 5,492,750.

0032An exemplary non-limiting coating <b>30</b> suitable for the invention is shown in <figref idref="DRAWINGS">FIG. 3</figref>. This exemplary coating <b>30</b> includes a base layer or first dielectric layer <b>40</b> deposited over at least a portion of a major surface of a substrate (e.g., the No. <b>2</b> surface <b>16</b> of the first ply <b>12</b>). The first dielectric layer <b>40</b> can comprise one or more films of antireflective materials and/or dielectric materials, such as but not limited to metal oxides, oxides of metal alloys, nitrides, oxynitrides, or mixtures thereof. The first dielectric layer <b>40</b> can be transparent to visible light. Examples of suitable metal oxides for the first dielectric layer <b>40</b> include oxides of titanium, hafnium, zirconium, niobium, zinc, bismuth, lead, indium, tin, and mixtures thereof. These metal oxides can have small amounts of other materials, such as manganese in bismuth oxide, tin in indium oxide, etc. Additionally, oxides of metal alloys or metal mixtures can be used, such as oxides containing zinc and tin (e.g., zinc stannate), oxides of indium-tin alloys, silicon nitrides, silicon aluminum nitrides, or aluminum nitrides. Further, doped metal oxides, such as antimony or indium doped tin oxides or nickel or boron doped silicon oxides, can be used. The first dielectric layer <b>40</b> can be a substantially single phase film, such as a metal alloy oxide film, e.g., zinc stannate, or can be a mixture of phases composed of zinc and tin oxides or can be composed of a plurality of metal oxide films, such as those disclosed in U.S. Pat. Nos. 5,821,001; 4,898,789; and 4,898,790.

0033In the illustrated exemplary embodiment shown in <figref idref="DRAWINGS">FIG. 3</figref>, the first dielectric layer <b>40</b> can comprise a multi-film structure having a first film <b>42</b>, e.g., a metal alloy oxide film, deposited over at least a portion of the inner major surface <b>16</b> of the first ply <b>12</b> and a second film <b>44</b>, e.g., a metal oxide or oxide mixture film, deposited over the first metal alloy oxide film <b>42</b>. In one non-limiting embodiment, the first film <b>42</b> can be a zinc/tin alloy oxide. The zinc/tin alloy oxide can be that obtained from magnetron sputtering vacuum deposition from a cathode of zinc and tin that can comprise zinc and tin in proportions of 10 wt. % to 90 wt. % zinc and 90 wt. % to 10 wt. % tin. One suitable metal alloy oxide that can be present in the first film <b>42</b> is zinc stannate. By “zinc stannate” is meant a composition of Zn_xSn_1−xO_2−x(Formula 1) where “x” varies in the range of greater than 0 to less than 1. For instance, “x” can be greater than 0 and can be any fraction or decimal between greater than 0 to less than 1. For example where x=⅔, Formula 1 is Zn_2/3Sn_1/3O_4/3, which is more commonly described as “Zn₂SnO₄”. A zinc stannate-containing film has one or more of the forms of Formula 1 in a predominant amount in the film. In one non-limiting embodiment, the first film <b>42</b> comprises zinc stannate and has a thickness in the range of 100 Å to 500 Å, such as 150 Å to 400 Å, e.g., 200 Å to 300 Å, e.g., 260 Å.

0034The second film <b>44</b> can be a zinc-containing film, such as zinc oxide. The zinc oxide film can be deposited from a zinc cathode that includes other materials to improve the sputtering characteristics of the cathode. For example, the zinc cathode can include a small amount (e.g., less than 10 wt. %, such as greater than 0 to 5 wt. %) of tin to improve sputtering. In which case, the resultant zinc oxide film would include a small percentage of tin oxide, e.g., 0 to less than 10 wt. % tin oxide, e.g., 0 to 5 wt. % tin oxide. An oxide layer sputtered from a zinc/tin cathode having ninety-five percent zinc and five percent tin is written as Zn_0.95Sn_0.05O_1.05herein and is referred to as a zinc oxide film. The small amount of tin in the cathode (e.g., less than 10 wt. %) is believed to form a small amount of tin oxide in the predominantly zinc oxide-containing second film <b>44</b>. The second film <b>44</b> can have a thickness in the range of 50 Å to 200 Å, such as 75 Å to 150 Å, e.g., 100 Å. In one non-limiting embodiment in which the first film <b>42</b> is zinc stannate and the second film <b>44</b> is zinc oxide (Zn_0.95Sn_0.05O_1.05), the first dielectric layer <b>40</b> can have a total thickness of less than or equal to 1,000 Å, such as less than or equal to 500 Å, e.g., 300 Å to 450 Å, e.g., 350 Å to 425 Å, e.g., 400 Å.

0035A first heat and/or radiation reflective film or layer <b>46</b> can be deposited over the first dielectric layer <b>40</b>. The first reflective layer <b>46</b> can include a reflective metal, such as but not limited to metallic gold, copper, silver, or mixtures, alloys, or combinations thereof. In one embodiment, the first reflective layer <b>46</b> comprises a metallic silver layer having a thickness in the range of 25 Å to 300 Å, e.g., 50 Å to 300 Å, e.g., 50 Å to 200 Å, such as 70 Å to 150 Å, such as 100 Å to 150 Å, e.g., 130 Å.

0036A first primer film <b>48</b> can be deposited over the first reflective layer <b>46</b>. The first primer film <b>48</b> can be an oxygen-capturing material, such as titanium, that can be sacrificial during the deposition process to prevent degradation or oxidation of the first reflective layer <b>46</b> during the sputtering process or subsequent heating processes. The oxygen-capturing material can be chosen to oxidize before the material of the first reflective layer <b>46</b>. If titanium is used as the first primer film <b>48</b>, the titanium would preferentially oxidize to titanium dioxide before oxidation of the underlying silver layer. In one embodiment, the first primer film <b>48</b> is titanium having a thickness in the range of 5 Å to 50 Å, e.g., 10 Å to 40 Å, e.g., 15 Å to 25 Å, e.g., 20 Å.

0037An optional second dielectric layer <b>50</b> can be deposited over the first reflective layer <b>46</b> (e.g., over the first primer film <b>48</b>). The second dielectric layer <b>50</b> can comprise one or more metal oxide or metal alloy oxide-containing films, such as those described above with respect to the first dielectric layer. In the illustrated non-limiting embodiment, the second dielectric layer <b>50</b> includes a first metal oxide film <b>52</b>, e.g., a zinc oxide (Zn_0.95Sn_0.05O_1.05) film deposited over the first primer film <b>48</b>. A second metal alloy oxide film <b>54</b>, e.g., a zinc stannate (Zn₂SnO₄) film, can be deposited over the first zinc oxide (Zn_0.95Sn_0.05O_1.05) film <b>52</b>. A third metal oxide film <b>56</b>, e.g., another zinc/tin oxide layer (Zn_0.95Sn_0.05O_1.05), can be deposited over the zinc stannate layer to form a multi-film second dielectric layer <b>50</b>. In one non-limiting embodiment, the zinc oxide (Zn_0.95Sn_0.05O_1.05) films <b>52</b>, <b>56</b> of the second dielectric layer <b>50</b> can each have a thickness in the range of about 50 Å to 200 Å, e.g., 75 Å to 150 Å, e.g., 100 Å. The metal alloy oxide layer (zinc stannate) <b>54</b> can have a thickness in the range of 100 Å to 800 Å, e.g., 200 Å to 700 Å, e.g., 300 Å to 600 Å, e.g., 550 Å to 600 Å.

0038An optional second heat and/or radiation reflective layer <b>58</b> can be deposited over the second dielectric layer <b>50</b>. The second reflective layer <b>58</b> can include any one or more of the reflective materials described above with respect to the first reflective layer <b>46</b>. In one non-limiting embodiment, the second reflective layer <b>58</b> comprises silver having a thickness in the range of 25 Å to 200 Å, e.g., 50 Å to 150 Å, e.g., 80 Å to 150 Å, e.g., 100 Å to 150 Å, e.g., 130 Å. In another non-limiting embodiment, this second reflective layer <b>58</b> can be thicker than the first and/or third reflective layers (the third reflective layer to be discussed later).

0039An optional second primer film <b>60</b> can be deposited over the second reflective layer <b>58</b>. The second primer film <b>60</b> can be any of the materials described above with respect to the first primer film <b>48</b>. In one non-limiting embodiment, the second primer film includes titanium having a thickness in the range of about 5 Å to 50 Å, e.g., 10 Å to 25 Å, e.g., 15 Å to 25 Å, e.g., 20 Å.

0040An optional third dielectric layer <b>62</b> can be deposited over the second reflective layer <b>58</b> (e.g., over the second primer film <b>60</b>). The third dielectric layer <b>62</b> can also include one or more metal oxide or metal alloy oxide-containing layers, such as discussed above with respect to the first and second dielectric layers <b>40</b>, <b>50</b>. In one non-limiting embodiment, the third dielectric layer <b>62</b> is a multi-film layer similar to the second dielectric layer <b>50</b>. For example, the third dielectric layer <b>62</b> can include a first metal oxide layer <b>64</b>, e.g., a zinc oxide (Zn_0.95Sn_0.05O_1.05) layer, a second metal alloy oxide-containing layer <b>66</b>, e.g., a zinc stannate layer (Zn₂SnO₄), deposited over the zinc oxide layer <b>64</b>, and a third metal oxide layer <b>68</b>, e.g., another zinc oxide (Zn_0.95Sn_0.05O_1.05) layer, deposited over the zinc stannate layer <b>66</b>. In one non-limiting embodiment, the zinc oxide layers <b>64</b>, <b>68</b> can have thicknesses in the range of 50 Å to 200 Å, such as 75 Å to 150 Å, e.g., 100 Å. The metal alloy oxide layer <b>66</b> can have a thickness in the range of 100 Å to 800 Å, e.g., 200 Å to 700 Å, e.g., 300 Å to 600 Å, e.g., 550 Å to 600 Å.

0041In one non-limiting aspect of the invention, the second dielectric layer <b>50</b> and third dielectric layer <b>62</b> have thicknesses that are within 10% of each other, such as within 5%, such as within 2% to 3% of each other.

0042The coating <b>30</b> can further include an optional third heat and/or radiation reflective layer <b>70</b> deposited over the third dielectric layer <b>62</b>. The third reflective layer <b>70</b> can be of any of the materials discussed above with respect to the first and second reflective layers. In one non-limiting embodiment, the third reflective layer <b>70</b> includes silver and has a thickness in the range of 25 Å to 300 Å, e.g., 50 Å to 300 Å, e.g., 50 Å to 200 Å, such as 70 Å to 150 Å, such as 100 Å to 150 Å, e.g., 120 Å. In one non-limiting embodiment, when the first, second, and/or third reflective layers have or contain silver, the total amount of silver for the coating <b>30</b> can range in the amount of 29 to 44 micrograms per centimeters²(ugm/cm²), such as 36.5 ugm/cm². In one non-limiting aspect of the invention, the first reflective layer <b>46</b> and third reflective layer <b>70</b> have thicknesses that are within 10% of each other, such as within 5%, such as within 2% to 3% of each other.

0043An optional third primer film <b>72</b> can be deposited over the third reflective layer <b>70</b>. The third primer film <b>72</b> can be of any of the primer materials described above with respect to the first or second primer films. In one non-limiting embodiment, the third primer film is titanium and has a thickness in the range of 5 Å to 50 Å, e.g., 10 Å to 25 Å, e.g., 20 Å.

0044An optional fourth dielectric layer <b>74</b> can be deposited over the third reflective layer (e.g., over the third primer film <b>72</b>). The fourth dielectric layer <b>74</b> can be comprised of one or more metal oxide or metal alloy oxide-containing layers, such as those discussed above with respect to the first, second, or third dielectric layers <b>40</b>, <b>50</b>, <b>62</b>. In one non-limiting embodiment, the fourth dielectric layer <b>74</b> is a multi-film layer having a first metal oxide layer <b>76</b>, e.g., a zinc oxide (Zn_0.95Sn_0.05O_1.05) layer, deposited over the third primer film <b>72</b>, and a second metal alloy oxide layer <b>78</b>, e.g., a zinc stannate layer (Zn₂SnO₄), deposited over the zinc oxide layer <b>76</b>. The zinc oxide layer <b>76</b> can have a thickness in the range of 25 Å to 200 Å, such as 50 Å to 150 Å, such as 100 Å. The zinc stannate layer <b>78</b> can have a thickness in the range of 25 Å to 500 Å, e.g., 50 Å to 500 Å, e.g., 100 Å to 400 Å, e.g., 200 Å to 300 Å, e.g., 260 Å.

0045The coating <b>30</b> can contain additional groups of dielectric layer/reflective metal layer/primer layer units if desired. In one non-limiting embodiment, the coating <b>30</b> can contain up to five antireflective metal layers, e.g., up to five silver layers.

0046The coating <b>30</b> can include a protective overcoat <b>80</b>, which, for example in the non-limiting embodiment shown in <figref idref="DRAWINGS">FIG. 3</figref>, is deposited over the optional fourth dielectric layer <b>74</b> (if present), to assist in protecting the underlying layers, such as the antireflective layers, from mechanical and chemical attack during processing. The protective coating <b>80</b> can be an oxygen barrier coating layer to prevent or reduce the passage of ambient oxygen into the underlying layers of the coating <b>30</b>, such as during heating or bending. The protective coating <b>80</b> can be of any desired material or mixture of materials. In one exemplary embodiment, the protective coating <b>80</b> can include a layer having one or more metal oxide materials, such as but not limited to oxides of aluminum, silicon, or mixtures thereof. For example, the protective coating <b>80</b> can be a single coating layer comprising in the range of 0 wt. % to 100 wt. % alumina and/or 100 wt. % to 0 wt. % silica, such as 5 wt. % to 95 wt. % alumina and 95 wt. % to 5 wt. % silica, such as 10 wt. % to 90 wt. % alumina and 90 wt. % to 10 wt. % silica, such as 15 wt. % to 90 wt. % alumina and 85 wt. % to 10 wt. % silica, such as 50 wt. % to 75 wt. % alumina and 50 wt. % to 25 wt. % silica, such as 50 wt. % to 70 wt. % alumina and 50 wt. % to 30 wt. % silica, such as 35 wt. % to 100 wt. % alumina and 65 wt. % to 0 wt. % silica, e.g., 70 wt. % to 90 wt. % alumina and 30 wt. % to 10 wt. % silica, e.g., 75 wt. % to 85 wt. % alumina and 25 wt. % to 15 wt. % of silica, e.g., 88 wt. % alumina and 12 wt. % silica, e.g., 65 wt. % to 75 wt. % alumina and 35 wt. % to 25 wt. % silica, e.g., 70 wt. % alumina and 30 wt. % silica, e.g., 60 wt. % to less than 75 wt. % alumina and greater than 25 wt. % to 40 wt. % silica. Other materials, such as aluminum, chromium, hafnium, yttrium, nickel, boron, phosphorous, titanium, zirconium, and/or oxides thereof, can also be present, such as to adjust the refractive index of the protective coating <b>80</b>. In one non-limiting embodiment, the refractive index of the protective coating <b>80</b> can be in the range of 1 to 3, such as 1 to 2, such as 1.4 to 2, such as 1.4 to 1.8.

0047In one non-limiting embodiment, the protective coating <b>80</b> is a combination silica and alumina coating. The protective coating <b>80</b> can be sputtered from two cathodes (e.g., one silicon and one aluminum) or from a single cathode containing both silicon and aluminum. This silicon/aluminum oxide protective coating <b>80</b> can be written as Si_xAl_1−xO_1.5+x/2, where x can vary from greater than 0 to less than 1.

0048Alternatively, the protective coating <b>80</b> can be a multi-layer coating formed by separately formed layers of metal oxide materials, such as but not limited to a bilayer formed by one metal oxide-containing layer (e.g., a silica and/or alumina-containing first layer) formed over another metal oxide-containing layer (e.g., a silica and/or alumina-containing second layer). The individual layers of the multi-layer protective coating can be of any desired thickness.

0049The protective coating can be of any desired thickness. In one non-limiting embodiment, the protective coating <b>80</b> is a silicon/aluminum oxide coating (Si_xAl_1−xO_1.5+x/2) having a thickness in the range of 50 Å to 50,000 Å, such as 50 Å to 10,000 Å, such as 100 Å to 1,000 Å, e.g., 100 Å to 500 Å, such as 100 Å to 400 Å, such as 200 Å to 300 Å, such as 250 Å. Further, the protective coating <b>80</b> can be of non-uniform thickness. By “non-uniform thickness” is meant that the thickness of the protective coating <b>80</b> can vary over a given unit area, e.g., the protective coating <b>80</b> can have high and low spots or areas.

0050In another non-limiting embodiment, the protective coating <b>80</b> can comprise a first layer and a second layer formed over the first layer. In one specific non-limiting embodiment, the first layer can comprise alumina or a mixture or alloy comprising alumina and silica. For example, the first layer can comprise a silica/alumina mixture having greater than 5 wt. % alumina, such as greater than 10 wt. % alumina, such as greater than 15 wt. % alumina, such as greater than 30 wt. % alumina, such as greater than 40 wt. % alumina, such as 50 wt. % to 70 wt. % alumina, such as in the range of 70 wt. % to 100 wt. % alumina and 30 wt. % to 0 wt. % silica. In one non-limiting embodiment, the first layer can have a thickness in the range of greater than 0 Å to 1 micron, such as 50 Å to 100 Å, such as 100 Å to 250 Å, such as 101 Å to 250 Å, such as 100 Å to 150 Å, such as greater than 100 Å to 125 Å. The second layer can comprise silica or a mixture or alloy comprising silica and alumina. For example, the second layer can comprise a silica/alumina mixture having greater than 40 wt. % silica, such as greater than 50 wt. % silica, such as greater than 60 wt. % silica, such as greater than 70 wt. % silica, such as greater than 80 wt. % silica, such as in the range of 80 wt. % to 90 wt. % silica and 10 wt. % to 20 wt. % alumina, e.g., 85 wt. % silica and 15 wt. % alumina. In one non-limiting embodiment, the second layer can have a thickness in the range of greater than 0 Å to 2 microns, such as 50 Å to 5,000 Å, such as 50 Å to 2,000 Å, such as 100 Å to 1,000 Å, such as 300 Å to 500 Å, such as 350 Å to 400 Å. Non-limiting examples of suitable protective coatings are described, for example, in U.S. patent application Ser. Nos. 10/007,382; 10/133,805; 10/397,001; 10/422,094; 10/422,095; and 10/422,096.

0051The transparency <b>10</b> further includes an antireflective coating <b>32</b>, for example on the No. <b>4</b> surface <b>22</b> of the second ply <b>18</b>. In one non-limiting embodiment, the antireflective coating <b>32</b> comprises alternating layers of relatively high and low index of refraction materials. A “high” index of refraction material is any material having a higher index of refraction than that of the “low” index material. In one non-limiting embodiment, the low index of refraction material is a material having an index of refraction of less than or equal to 1.75. Non-limiting examples of such materials include silica, alumina, and mixtures or combinations thereof. The high index of refraction material is a material having an index of refraction of greater than 1.75. Non-limiting examples of such materials include zirconia and zinc stannate. The antireflective coating <b>32</b> can be, for example but not limiting to the present invention, a multi-layer coating as shown in <figref idref="DRAWINGS">FIG. 4</figref> having a first metal alloy oxide layer <b>86</b> (first layer), a second metal oxide layer <b>88</b> (second layer), a third metal alloy oxide layer <b>90</b> (third layer), and a metal oxide top layer <b>92</b> (fourth layer). In one non-limiting embodiment, the fourth layer <b>92</b> (upper low index layer) comprises silica or alumina or a mixture or combination thereof, the third layer <b>90</b> (upper high index layer) comprises zinc stannate or zirconia or mixtures or combinations thereof, the second layer <b>88</b> (bottom low index layer) comprises silica or alumina or a mixture or combination thereof, and the first layer <b>86</b> (bottom high index layer) comprises zinc stannate or zirconia or mixtures or combinations thereof. In one non-limiting embodiment, the top layer <b>92</b> comprises silica and ranges from 0.7 to 1.5 quarter wave, e.g., 0.71 to 1.45 quarter wave, such as 0.8 to 1.3 quarter wave, such as 0.9 to 1.1 quarter wave. By “quarter wave” is meant: physical layer thickness·4·refractive index/(reference wavelength of light). In this discussion, the reference wavelength of light is 550 nm. In this non-limiting embodiment, the thickness of the upper high index layer <b>90</b> is defined by the formula:−0.3987·(quarter wave value of top layer)²−1.1576·(quarter wave value of top layer)+2.7462. Thus, if the top layer <b>92</b> is 0.96 quarter wave, the upper high index layer <b>90</b> would be −0.3987(0.96)²−1.1576(0.96)+2.7462=1.2675 quarter wave. The bottom low index layer <b>88</b> is defined by the formula: 2.0567·(quarter wave value of top layer)²−3.5663·(quarter wave value of top layer)+1.8467. The bottom high index layer <b>86</b> is defined by the formula: −2.1643·(quarter wave value of top layer)²+4.6684·(quarter wave value of top layer)−2.2187. In one specific non-limiting embodiment, the antireflective coating <b>32</b> comprises a top layer <b>92</b> of silica of 0.96 quarter wave (88.83 nm), a layer <b>90</b> of zinc stannate of 1.2675 quarter wave (84.72 nm), a layer <b>88</b> of silica of 0.3184 quarter wave (29.46 nm), and a layer <b>86</b> of zinc stannate of 0.2683 quarter wave (17.94 nm). In other non-limiting embodiments, the quarter wave values of the layers <b>86</b>, <b>88</b>, and <b>90</b> can vary by ±25% from the formula values above, such as ±10%, such as ±5%.

0052Other suitable antireflective coatings are disclosed in U.S. Pat. No. 6,265,076 at column 2, line 53 to column 3, line 38; and Examples 1-3. Further suitable antireflective coatings are disclosed in U.S. Pat. No. 6,570,709 at column 2, line 64 to column 5, line 22; column 8, lines 12-30; column 10, line 65 to column 11, line 11; column 13, line 7 to column 14, line 46; column 16, lines 3548; column 19, line 62 to column 21, line 4; Examples 1-13; and Tables 1-8.

0053In the non-limiting embodiment illustrated in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, the bus bar assembly <b>36</b> includes a first or bottom bus bar <b>96</b> and a second or top bus bar <b>98</b> formed on the inner surface <b>16</b> of the outer ply <b>12</b> and separated by a bus bar to bus bar distance D. The bus bars <b>96</b>, <b>98</b> are in electrical contact with the conductive coating <b>30</b>. The bus bar assembly also includes a first conductive lead or strip <b>100</b> connected to the first bus bar <b>96</b> and a second conductive lead or strip <b>102</b> connected to the second bus bar <b>98</b>. Each of the leads <b>100</b>,<b>102</b> is connected to the power source <b>38</b>. The bus bars <b>96</b>, <b>98</b> and/or the conductive strips <b>100</b>, <b>102</b> can be formed of conductive metal foil or strips (such as but not limited to copper foil or tinned copper foil), or can be formed by conductive coatings (such as ceramic coatings), or combinations thereof. In one non-limiting embodiment of the invention, bus bars <b>96</b> and <b>98</b> can be positioned at least partially on, or completely on, the decorative band <b>26</b> (as shown in <figref idref="DRAWINGS">FIG. 2</figref>).

0054The power source <b>38</b> can be any conventional power source. However, in one non-limiting embodiment, the power source <b>38</b> is a conventional vehicle alternator configured to supply in the range of 13 volts to 15 volts, e.g., approximately 14 volts.

0055A further transparency <b>106</b> incorporating features of the present invention is shown in <figref idref="DRAWINGS">FIG. 5</figref>. The construction of transparency <b>106</b> is similar to the transparency <b>10</b> but the coating <b>30</b> includes one or more “cut-out” areas, such as cut-outs <b>108</b> and <b>110</b>. The cut outs <b>108</b> and <b>110</b> divide the coating <b>30</b> into a first major portion <b>114</b>, a second major portion <b>116</b>, and a central portion <b>118</b>. The bus bar assembly <b>120</b> in this non-limiting embodiment is a quad-feed assembly, i.e., has four connectors <b>122</b>, <b>124</b>, <b>126</b>, and <b>128</b> connected to four bus bars <b>130</b>, <b>132</b>,<b>134</b>, and <b>136</b>, respectively. Bus bars <b>130</b> and <b>132</b> provide power primarily to the first major portion <b>114</b> and bus bars <b>134</b> and <b>136</b> provide power primarily to the second major region <b>116</b>.

0056In one non-limiting embodiment of the invention, the coating <b>30</b> is configured or dimensioned to provide a power density of 2 to 10 watts per decimeter²(W/dm²) at a bus bar to bus bar distance D (see <figref idref="DRAWINGS">FIG. 1</figref>) in the range of 24 inches to 30 inches (60 cm to 75 cm), such as 4 to 8 W/dm², such as 5 to 6 W/dm², when the coating is in electrical contact with a conventional vehicle alternator, such as a conventional alternator producing 80 amps and 14 volts. It is believed that such a power density is sufficient to melt ice found in contact with outer surface <b>14</b> of the substrate <b>10</b>. For vision panels (such as a windshield) in the United States, the transparency should also have a visible light transmittance of greater than or equal to 70%, such as greater than or equal to 71%. As will be appreciated by one skilled in the art, several different competing factors need to be balanced to provide a coating having sufficient conductivity and also sufficient transmittance. For example, as the distance D between the bus bars increases (i.e., the transparency becomes wider from top to bottom), the bus bar to bus bar resistance increases. As the bus bar to bus bar resistance increases, the power density decreases. In order to maintain the power density as the bus bar to bus bar distance is increased, the resistivity of the coating must decrease. One way of decreasing the resistivity is by increasing the thickness of one or more of the silver layers and/or by increasing the number of silver layers. In one non-limiting practice of the invention, the thickness and/or number of silver layers is configured to give a total resistivity for the coating of 0.6 to 1.7 Ω/□, such as 0.8 to 1.3 Ω/□, such as 0.9 to 1.1 Ω/□. However, as will also be appreciated by one skilled in the art, as the number or thickness of the silver layers increases, the visible light transmittance decreases. For forward vision areas of a vehicle, such as a windshield, the thickness and/or number of silver layers should not be increased to the point where visible light transmittance of the vision area falls below about 70%.

0057It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.